Methods of forming physical vapor deposition target/backing plate assemblies

ABSTRACT

The invention encompasses PVD target/backing plate assemblies which include a PVD target having a surface, and a bonding layer on the surface. The bonding layer has a different composition than the target surface, and a backing plate is provided to be separated from the PVD target surface by at least the bonding layer. The bonding layer forms a strong diffusion bond to the target. The invention also includes methods of forming PVD target/backing plate assemblies. Additionally, the invention includes assemblies in which one or more of titanium, zirconium, and copper is incorporated into a bonding layer between a target and a backing plate in a physical vapor deposition target/backing assembly.

RELATED PATENT DATA

This patent is a divisional application of U.S. patent application Ser.No. 09/699,899 which was filed on Oct. 27, 2000 now U.S. Pat. No.6,376,281.

TECHNICAL FIELD

The invention pertains to physical vapor deposition target/backing plateassemblies, and to methods of forming physical vapor depositiontarget/backing plate assemblies. In particular applications, theinvention pertains to methods of incorporating a bonding layer between atarget and a backing plate in a physical vapor deposition target/backingassembly, with an exemplary bonding layer being a layer capable offorming a strong diffusion bond to the target at a temperature of lessthan or equal to about 500° C. in a time of less than or equal to about24 hours. A “strong” diffusion bond is defined as a bond capable ofpassing a peel test described herein. In further applications, theinvention pertains to methods of incorporating one or more of titanium,zirconium, and copper in a bonding layer between a target and a backingplate in a physical vapor deposition target/backing assembly.

BACKGROUND OF THE INVENTION

Physical Vapor Deposition (PVD) targets have wide application infabrication processes where thin films are desired, and include, forexample, sputtering targets. An exemplary PVD process is a sputteringprocess, and an exemplary application of a PVD process is to form thinfilms across semiconductor substrates in semiconductor processingapplications.

A prior art PVD process is diagrammatically illustrated in FIG. 1. Morespecifically, FIG. 1 illustrates an apparatus 10 comprising a PVDtarget/backing plate assembly 12 above a substrate 14. Assembly 12comprises a sputtering target 16 joined to a backing plate 18. Target 16can comprise any of numerous metallic elements and alloys, and backingplate 18 can comprise numerous electrically and thermally conductivematerials, such as, for example, copper or aluminum.

Target 16 has a surface 20 from which material is ejected, and which canbe referred to as a sputtering surface. In operation, surface 20 isexposed to ions or atoms which impact the surface and are utilized toeject material from the surface toward substrate 14. The ejectedmaterial is illustrated by arrows 22 in FIG. 1. Such ejected materiallands on substrate 14 to form a thin film (not shown) over thesubstrate.

Backing plate 18 provides several functions during the sputteringapplication illustrated in FIG. 1. For instance, backing plate 18 istypically provided with a shape configured to enable assembly 12 to beremovably retained within a sputtering apparatus chamber (not shown).Also, backing plate 18 is typically formed of an electrically/thermallyconductive material and is utilized for passing an electric field tosputtering target 16. An interface between target 16 and backing plate18 should preferably comprise a bond strong enough to retain target 16to backing plate 18 during a sputtering operation, and yet also comprisea continuous, uniform and electrically conductive construction so thatan electric field can be passed uniformly across the interface frombacking plate 18 to target 16. Among the methodologies presentlyutilized for forming a target-to-backing plate interface is amethodology of providing solder (shown as 15 in FIG. 1) between a targetand backing plate to bond the target to the backing plate. The soldercan comprise, for example, one or both of tin and indium.

A difficulty in utilizing solders is that the solders frequently do notadhere well to a target material, and accordingly a target can separatefrom a backing plate if only solder is utilized in the backingplate/target bond. Such problem can be particularly pronounced withtargets comprising one or more of tantalum, cobalt, zirconium, platinum,iron, niobium, molybdenum, chromium, aluminum, copper and manganese. Inorder to overcome such difficulty, a transition layer 19 is frequentlyprovided over a target surface prior to bonding the target surface to abacking plate. In the shown target/backing plate construction, target 16has a surface 17 which is ultimately to be utilized in forming a bondwith backing plate 18. Transition layer 19 is formed over surface 17prior to bonding the target with the backing plate.

Transition layer 19 typically comprises nickel. The nickel is consideredto adhere better to various target materials than does an indium ortin-based solder, and in turn an indium or tin-based solder isconsidered to adhere better to the nickel than to the target material.Accordingly, the nickel layer 19 can be ultimately bonded with solder 15to retain the target 16 to backing plate 18.

Nickel-containing transition layers improve adhesion of various targetmaterials to backing plates. However, it is found that even when suchlayers are provided, problems can still be encountered with separationor delamination of a PVD target from a target/backing plate assemblyduring a sputtering process. Nickel-containing transition layers can beparticularly unsatisfactory when utilized with target compositionscomprising one or more of Ta, Co, Zr, Pt, Fe, Nb, Mn, Cr, Al, Cu. Theseparation of a target and backing plate can occur, for example, at aninterface between the nickel transition layer and the target. Ifdelamination exceeds more than about 5% of the area of a target surface,the target/backing plate assembly can be rendered inoperable in that itwill not perform within desired parameters. In some instances, adelamination of greater than or equal to about 1% can render atarget/backing plate assembly inoperable. It would, accordingly, bedesirable to develop new methodologies for adhering targets to backingplates to avoid the delamination problems associated with nickeltransition layers.

SUMMARY OF THE INVENTION

In one aspect, the invention comprises a PVD target/backing plateassembly. The assembly includes a PVD target having a surface, and abonding layer on the surface. The bonding layer has a differentcomposition than the target surface, and a backing plate is provided tobe separated from the PVD target surface by at least the bonding layer.The bonding layer can comprise a material capable of forming a strongdiffusion bond to the target in less than or equal to about 24 hours ata temperature of less than or equal to about 500° C., and can comprise,for example, one or more of copper, titanium and zirconium. Inparticular embodiments, the bonding layer can consist of, or consistessentially of, one or more of copper, titanium and zirconium. A“strong” diffusion bond is defined as a bond capable of passing a peeltest described herein.

In another aspect, the invention includes a method of forming a PVDtarget/backing plate assembly. A bonding layer is formed on a surface ofa PVD target, and a backing plate is joined to the bonding layer.Accordingly, the backing plate is separated from the PVD target surfaceby at least the bonding layer. The bonding layer can comprise, forexample, one or more of copper, titanium and zirconium.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic, cross-sectional view of a portion of a priorart PVD apparatus.

FIG. 2 is a diagrammatic, cross-sectional view of a PVD target at apreliminary processing step of a method of the present invention.

FIG. 3 is a view of the FIG. 2 target shown at a processing stepsubsequent to that of FIG. 2.

FIG. 4 is a view of the FIG. 2 target shown at a processing stepsubsequent to that of FIG. 3.

FIG. 5 is a view of the FIG. 2 target shown at a processing stepsubsequent to that of FIG. 4.

FIG. 6 is a view of the FIG. 2 targets shown at a processing stepsubsequent to that of FIG. 5, and shown in a PVD target/backing plateassembly.

FIG. 7 is a top view of the assembly of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention encompasses new methods of forming target/backing plateassemblies, and also encompasses target/backing plate assemblies whichcan be formed by the methods. Methodology of the present invention canbe utilized with numerous metallic PVD target compositions, including,for example, compositions comprising one or more transition metals, aswell as compositions comprising one or more of Tl and Al. Methodology ofthe present invention can have particular applicability to PVD targetscomprising one or more of tantalum, cobalt, zirconium, platinum, iron,niobium, manganese, chromium, aluminum and copper; as such compositionscan cause particular difficulties with respect to prior artmethodologies described in the “Background” section of this disclosurewhich can be overcome with methodology of the present invention.Further, methodology of the present invention can be particularlyapplicable for PVD targets which consist essentially of, or consist of,Ta, Co, CoTaZr, CoPt, Pt, FeTa, TiZr, CoNb, Mo, CoCrPt, Al, AlCuFe, FeMnand FeAl. It is to be understood that the listed complexes, such as, forexample, CoTaZr, are described in terms of the components of thecomplexes, rather than stoichiometries. For instance, numerous complexesconsisting of, or consisting essentially of, CoTaZr in variousstoichiometric relationships can exist, and the nomenclature “CoTaZr” isintended to encompass all of such complexes.

An exemplary method of the present invention is described with referenceto FIGS. 2-7. Referring initially to FIG. 2, a PVD target 30 isillustrated in cross-sectional view. Target 30 comprises a sputteringsurface 32 and a back surface 34 in opposing relation to sputteringsurface 32. Back surface 34 is shown to comprise surface anomalies 36which can correspond to, for example, burrs, contaminants, or otheraspects of surface roughness. Features 36 are shown at an exaggeratedscale relative to target 30 to enable illustration of features 36. It isto be understood that features 36 would normally be much smaller inrelation to target 30 than shown.

FIG. 3 illustrates target 30 after surface 34 has been subjected to acleaning procedure. An exemplary cleaning procedure comprises firstcleaning the surface with a solvent to remove debris from the surface,and subsequently exposing the surface to a plasma etch to remove burrsor other non-desired surface features, and accordingly smooth surface34. A solvent is preferably chosen which is substantially inert relativeto reaction with the material of target 30 to avoid oxidation and/orcorrosion of target 30 at surface 34, with an exemplary solvent being anorganic solvent, such as, isopropyl alcohol. A suitable plasma etch canbe conducted with an argon plasma at 1200 volts for a time of about 20minutes. The etch is preferably conducted at a sub-atmospheric pressure,such as, for example, a pressure of about 10⁻⁶ torr.

Referring to FIG. 4, a bonding layer 40 is provided on surface 36 oftarget 30. Bonding layer 40 can comprise, for example, one or more oftitanium, copper, and zirconium; and in particular embodiments canconsist essentially of, or consist of, one or more of titanium,zirconium or copper. Bonding layer 40 can ultimately form a strong bondto target 30, and can, for example, be a layer capable of forming astrong diffusion bond to the target in less than or equal to about 24hours at a temperature of less than or equal to about 500° C. A “strong”diffusion bond is defined as a bond capable of passing a peel testdescribed herein.

In an exemplary embodiment, layer 40 comprises titanium. Such exemplaryembodiment is described below by referring to layer 40 as atitanium-comprising layer 40. It is to be understood, however, that theinvention can be utilized with other materials besides a referred-totitanium-comprising layer, and that the described processing can also beutilized in conjunction with, for example, a zirconium-comprising layer40 or a copper-comprising layer 40.

With reference to the exemplary embodiment in which layer 40 comprisestitanium, the titanium-comprising layer 40 can have titanium as amajority element (with the term “majority element” indicating thattitanium is present in a higher concentration than in any other element,and can include, for example, a material having 30 weight % titanium,provided, that no other element is present to a concentration of greaterthan or equal to 30 weight %), can consist essentially of titanium, orcan consist of titanium. If layer 40 and target 30 both comprisetitanium, layer 40 can comprise a different composition of titanium thandoes target 30.

An exemplary process of forming layer 40 is ion deposition.Specifically, target 30 can be placed in a vacuum chamber at asub-atmospheric pressure, such as, for example, a pressure of 10⁻⁶ torr,and provided with either a positive or negative charge. If layer 40 isto comprise titanium, a titanium substrate can be provided with anopposite charge to that of target 30 and exposed to an electron beamgun. Titanium will then vaporize from the substrate and impact thetarget. Ion deposition processes are known in the art. Ion deposition isan exemplary process for forming titanium layer 40, and is but one ofseveral technologies that can be utilized for forming titanium layer 40.Another process that can be utilized for forming layer 40 iselectroplating.

One aspect of an ion deposition process can be that coating materialsdriven by the process can actually penetrate a short distance intosurface 36 of target 30, as well as forming coating 40 over surface 36.Coating 40 can be formed to a thickness of, for example, from about2,000 angstroms to about 4,000 angstroms, with an exemplary thicknessbeing about 3,000 angstroms. At some time during or after formation ofcoating 40, the material of coating 40 can be diffusion bonded to target30. Such diffusion bonding preferably occurs at a temperature of lessthan 500° C. (such as, for example, a temperature of less than or equalto 200° C.), for a time of less than or equal to 24 hours (such as, forexample, a time of a few hours). The diffusion bonding preferably formsa strong bond, with “strong” being defined as a bond that passes a peeltest described herein.

If ion deposition is used to form layer 40, the diffusion bonding canoccur during the ion deposition. It can be advantageous to havediffusion bonding occurring during a deposition process, as such cansave processing steps relative to embodiments in which diffusion bondingoccurs in a separate step from a deposition process.

Since the plasma cleaning (described with reference to FIG. 3) and thetitanium coating (described with reference to FIG. 4) can both beconducted at sub-atmospheric pressure, target 30 can be maintained undersub-atmospheric pressure conditions from the time that the plasmacleaning step is initiated until the ion deposition is complete.

If material 40 comprises a readily-oxidized material (such as titanium),it can be desired to form a protective (or passivating) layer overmaterial 40 to alleviate oxidation of the material of layer 40. FIG. 5illustrates formation of a passivating layer 42 over layer 40.Passivating layer 42 can comprise, for example, nickel, and can beformed by, for example, ion deposition of nickel. In the shownembodiment, layer 40 comprises an upper surface 41 and sidewall surfaces43; and passivating layer 42 is formed only over upper surface 41. It isto be understood, however, that the invention encompasses otherembodiments wherein passivating layer 42 is also formed over sidewallsurfaces 43. Passivating layer 42 is preferably at least 1200 angstromsthick, and can be, for example, at least 1500 angstroms thick.

In embodiments in which passivating layer 42 is formed by iondeposition, the passivating layer can be formed at a sub-atmosphericpressure, such as, for example, a pressure of 10⁻⁶ torr. Accordingly,target 34 can remain under a sub-atmospheric pressure from a time ofinitiation of the plasma cleaning step (described with reference to FIG.3) until after formation of passivating layer 42. Such can reduceexposure of target 30 to atmosphere-borne contaminants.

Referring to FIG. 6, a layer of solder 44 is provided over passivatinglayer 42. Solder layer 44 can comprise, for example, one or both of tinand indium. A backing plate 46 is provided against solder 44, and bondedthrough solder 44 to the assembly comprising target 30, and layers 40and 42. Backing plate 46 can comprise, for example, copper. Solder 44can be formed to, for example, a thickness of at least about 10,000 Å.An exemplary method of forming solder 44 comprises applying a firstportion of solder to nickel layer 44, and subsequently heating thenickel to about 200° C. Subsequently, a second portion of solder isapplied on the first portion, and the two portions of solder are pressedbetween backing plate 46 and target 30 in assembly 50. The solder is ina softened or heated form during the pressing of the solder withinassembly 50. The assembly is clamped together, and allowed to cool for 4to 5 hours to achieve a solder bond holding backing plate 46 to layer42. Such bond can alternatively be referred to as a bond in whichbacking plate 46 is held to target 30 through solder layer 44,passivating layer 42, and bonding layer 40. The assembly 50 of FIG. 6can be referred to as a PVD target/backing plate assembly.

Assembly 50 differs from the prior art target/backing plate assembly 12(FIG. 1), in that assembly 50 comprises a titanium-comprising layer 40(or another bonding layer 40 encompassed by the present invention) inplace of nickel-comprising transition layer 19 of the prior artassembly. Assembly 50 can alternatively be considered as comprising abacking plate 46 separated from a target 30 by at least bonding layer40. In the shown embodiment, backing plate 46 is actually separated fromtarget 30 by not only bonding layer 40, but also by solder layer 44 andpassivating layer 42. However, it is to be understood that the inventionencompasses other embodiments (not shown) wherein one or both of layers44 and 42 can be eliminated. For instance, bonding layer 40 can bebonded directly to backing plate 46 utilizing diffusion-bondingmethodologies.

Bonding layer 40 is distinct from target 30 in that bonding layer 40comprises a different composition than target 30. Bonding layer 40 canhave a different composition than target 30 if it comprises overlappingmaterials with target 30, but in different concentrations than target30; or if it comprises different materials than target 30. An advantageof methodology of the present invention is that it can form strongdiffusion bonds between bonding layer 40 and target 30, even if layer 40and target 30 do not comprise a common majority element. For instance,bonding layer 40 can predominately comprise copper in applicationswherein target 30 does not comprise copper. As another example, layer 40can predominately comprise titanium in applications wherein target 30does not comprise titanium. As yet another example, layer 40 canpredominately comprise zirconium in applications wherein target 30 doesnot comprise zirconium.

An alternative view of assembly 50, in constructions in whichpassivating layer 42 comprises nickel, is that assembly 50 can beconsidered to comprise the nickel-comprising transition layer of theprior assembly 12 of FIG. 1, but to comprise such layer as anickel-comprising layer 42 separated from target 30 by bonding layer 40.

An advantage of utilizing titanium, zirconium and/or copper in bondinglayers of the present invention is that such materials can be compatiblefor forming strong bonding interactions with numerous metals and alloys,including transition metals, thallium and aluminum. For instance,titanium can be compatible with the metals and alloys relative to, forexample, thermal expansion. In peel tests, a layer 40 of titanium hasbeen found to have excellent adhesion to a target 30. To perform thepeel test, a 15 millimeter wide strip of Nichiban™ Clear Tape wasmanually pressed on solder 44 along a diameter of target plate 30 in aconstruction which included solder 44, a nickel-comprising passivatinglayer 42, titanium-comprising layer 40 and a target 30 comprisingcobalt/tantalum/zirconium, with such construction not yet being bondedto a backing plate. The tape was then peeled from the solder layer, andthe amount that adhered to the tape was observed. The test was repeatedby applying a second strip of tape along a diameter oriented 90° to thediameter where the first test was performed. Examination of the stripsof tape revealed that none of the material from either the solder layer44, nickel-comprising layer 42, titanium-comprising layer 40 or target30 had adhered to the tape, indicating excellent adhesion betweentitanium layer 40 and target 30. A bonding layer is defined to form a“strong” bond to a target if the bonding layer can pass theabove-described peel test. In other words, if the bonding layer adheressufficiently to the target that none of the bonding layer is lifted fromthe target by Nichiban™ Clear Tape that is applied and lifted from twoperpendicular directions across a surface of the bonding layer. The tapecan be applied directly to the bonding layer, or to one or more layersadhered over the bonding layer. Preferably, the tape is applied directlyto the bonding layer. If the tape is applied to one or more layersadhered over the bonding layer, the test can be inconclusive if the oneor more layers separate from one another, rather than allowingsufficient stress to be imparted to the bonding layer to determine ifthe bonding layer will separate from the target.

Although target constructions comprising any of numerous elements andcompositions can be utilized in methodology of the present invention,some elements and compositions can be less preferred than others due to,for example, some elements and compositions forming weaker bonds withbonding layer 40 than other elements and compositions. For instance,targets comprising indium-tin-oxide (ITO) can be less preferred thanother targets for utilization in methodology of the present invention.

FIG. 7 is a top view of the FIG. 6 assembly 50, and illustrates thatassembly 50 can, in particular embodiments, comprise a round outerperipheral shape. It is noted that FIGS. 2-7 are exemplary embodimentsof the present invention only, and that other shapes of backing platesand targets can be utilized in methodology of the present inventionbesides the shapes specifically shown.

Although various aspects of the invention are described above withreference to the exemplary embodiment in which layer 40 comprisestitanium, it is to be understood that similar processing can be utilizedif bonding layer 40 comprises other materials such as, for example,zirconium or copper. If layer 40 comprises zirconium, the layer can havezirconium as a majority element, can consist essentially of zirconium,or can consist of zirconium. If layer 40 comprises copper, the layer canhave copper as a majority element, can consist essentially of copper, orcan consist of copper.

What is claimed is:
 1. A method of forming a PVD target/backing plateassembly, comprising: forming a bonding layer on a surface of the PVDtarget and forming a strong diffusion bond between the bonding layer andthe target in less than or equal to about 24 hours at a temperature ofless than or equal to about 500° C.; the forming the bonding layercomprising coating the bonding layer onto the surface by ion deposition;the strong diffusion bond forming during the ion deposition; forming apassivating layer on the bonding layer; forming a layer of solder on thepassivating layer; and joining a backing plate to the target, thejoining the backing plate to the target comprising bonding the backingplate with the solder, the backing plate being joined through aconnection that includes at least the bonding layer and accordinglybeing separated from the PVD target surface by at least the bondinglayer.
 2. The method of claim 1 further comprising exposing the surfaceof the PVD target to a plasma etch before forming the bonding layer. 3.The method of claim 2 wherein the PVD target remains exposed to asub-atmospheric pressure from the exposing of the target to a plasmaetch until the forming the layer of solder.
 4. The method of claim 3wherein the passivating layer comprises nickel.
 5. The method of claim 1wherein titanium is a majority element of the bonding layer.
 6. Themethod of claim 1 wherein the bonding layer consists essentially oftitanium.
 7. The method of claim 1 wherein zirconium is a majorityelement of the bonding layer.
 8. The method of claim 1 wherein thebonding layer consists essentially of zirconium.
 9. The method of claim1 wherein copper is a majority element of the bonding layer.
 10. Themethod of claim 1 wherein the bonding layer consists essentially ofcopper.
 11. The method of claim 1 wherein the PVD target comprises atleast one transition metal.
 12. The method of claim 1 wherein the PVDtarget comprises one or more of Tl, Ta, Co, Zr, Pt, Fe, Nb, Mn, Cr, Al,Cu.
 13. The method of claim 1 wherein the PVD target consistsessentially of Ta, Co, CoTaZr, CoPt, Pt, FeTa, TiZr, CoNb, Mo, CoCrPt,Al, AlCuFe, FeMn or FeAl; wherein the complexes are described in termsof components rather than stoichiometries.
 14. A method of forming a PVDtarget/backing plate assembly, comprising: forming a bonding layer on asurface of the PVD target, the bonding layer comprising one or both ofzirconium and titanium; and joining a backing plate to the target; thebacking plate being joined through a connection that includes at leastthe bonding layer and accordingly being separated from the PVD targetsurface by at least the bonding layer.
 15. The method of claim 14wherein the forming the bonding layer comprises coating the bondinglayer onto the surface by ion deposition.
 16. The method of claim 14further comprising exposing the surface of the PVD target to a plasmaetch before forming the bonding layer; wherein the forming the bondinglayer comprises coating the bonding layer onto the surface by iondeposition; and wherein the PVD target remains exposed to asub-atmospheric pressure during the exposing and coating.
 17. The methodof claim 16 further comprising: forming a passivating layer on thebonding layer; forming a layer of solder on the passivating layer; andwherein the joining the backing plate to the target comprises bondingthe backing plate with the solder; and the PVD target remains exposed toa sub-atmospheric pressure from the exposing of the target to a plasmaetch through at least until the step of forming the layer of solder. 18.The method of claim 17 wherein the passivating layer comprises nickel.19. The method of claim 14 wherein the forming the bonding layercomprises coating the bonding layer onto the surface by ion deposition;the method further comprising, before the forming the bonding layer:cleaning the surface with an organic solvent; and exposing the cleanedsurface to a plasma etch.
 20. The method of claim 14 wherein titanium isa majority element of the bonding layer.
 21. The method of claim 14wherein the bonding layer consists essentially of titanium.
 22. Themethod of claim 14 wherein zirconium is a majority element of thebonding layer.
 23. The method of claim 14 wherein the bonding layerconsists essentially of zirconium.
 24. The method of claim 14 furthercomprising: forming a passivating layer on the bonding layer; forming alayer of solder on the passivating layer; and wherein the joining thebacking plate to the target comprises bonding the backing plate with thesolder.
 25. The method of claim 14 wherein the PVD target comprises atleast one transition metal.
 26. The method of claim 14 wherein the PVDtarget comprises one or more of Tl, Ta, Co, Zr, Pt, Fe, Nb, Mn, Cr, Al,Cu.
 27. The method of claim 14 wherein the PVD target consistsessentially of Ta, Co, CoTaZr, CoPt, Pt, FeTa, TiZr, CoNb, Mo, CoCrPt,Al, AlCuFe, FeMn or FeAl; wherein the complexes are described in termsof components rather than stoichiometries.